Left button on my Toshiba Satellite keypad does nothing.

Have I simply worn out the button or could this be a software issue? I have tried the fn f5 solution, the "end task" solution in task manager with the keypad selected (using the right button on the keypad and or the return button on the keyboard) but nothing seems to work.

This laptop has seen a lot of use in the six years I have had it, so the left button which is used for practically everything could be physically dead. Any attempt at helping me is greatly appreciated!